Dipole antenna system



OV. 17, 1970 E. N. WILLIE ETAL 3541555 I DIPOLE ANTENNA SYSTEM FiledJune 21, 1967 3 Sheet-Sheet 1 FIG J, H62.

l 7 DELAY TRANS- LINE 6 7 FORMER 5 TRANS- 8 5 FORMER l4 g f m 9 IO in Iw/gwJ T553 Nov; 17, 19 70 N. WILLIE ETAL DIPOLE ANTENNA SYSTEM Fi1edJune 21, 1967 3 Sheets-Sheet 2 FIG] 4b 47 4a 49 so -I 17, 1970 E. N.WILLIE ETAL 3'541'555 DIPOLE ANTENNA SYSTEM Filed June 21 1967 3Sheets-Sheet 5 H09. FIGIC).

- I II b l. b I 7 4 8 7 TRANS- 8 TRANS- FORMER V FORMER |o3 FIGII.

rIOZ b 'I i TRANs- 8 .FQRMER United States Patent US. Cl. 343720 7Claims ABSTRACT OF THE DISCLOSURE A dipole antenna system wherein onearm of the dipole is fixed and the other arm may be randomly positionedand/or of random length including a phase adjustment device associatedwith one or both arms to maintain the signals from the two arms in thedesired phase relation.

Dipole antennas, when connected in the customary manner to thedifferential input terminals of a receiver, are subject to differentialphase errors between the dipoles arms. Such errors can, as it is wellunderstood, be caused by incidental reflectors and re-radiators,creating signal delays or advances in one dipole arm with reference tothe other; and partial or complete signal cancellations can ensue, evenif signal strength at the receivers location is relatively high.

-This familiar reception problem, which is probably best known as thecause of reception difficulties of television receivers with indoorantennas (rabbit ears), can be further aggravated if a non-symmetricaldipole is used," especially if one dipole arm is flexible meaning thatit can freely move in its direction and length, while the other armremains essentially fixed.

A good example, which will also be used to illustrate the nature of ourinvention, is a vertical or horizontal dipole in which one arm isrepresented by a power cord while the other arm is a stationarymonopole, attached to the inside or outside of the receiver. Power cordsare flexible and subject to random placement and prone to accidentalshifting, and means must therefore be provided for re-establishment oforiginal performance if such accidental shifting has occurred. Inaddition, a power cord, when used as an antenna, may differ in itslength more drastically from the ideal mid-band quarter-wave length ofits companion dipole arm, causing the receiver to perform poorly at somefreqeuncies only, while it is satisfactory on others.

The present invention eliminates the above-described problem throughrecognition of the following facts:

(1) If the second, flexible dipole arm does not properly match theeffective length of the first, fixed arm, it

is less the difference in signal amplitude, due to differing length,which causes intolerable signal losses, than major phase shifts betweenthe movable and the fixed arms signals. These phase shifts are capableof partially or completely disabling the receivers differential inputcircuit by being in less than exact phase-opposition and,

'in the ultimate case, approaching phase-identity.

tional indoor antenna would improve performance.

3,541,555 Patented Nov. 17, 1970 Accordingly, this invention providessuch a control; it does, however, not physically rotate, lengthen orshorten the flexible aerial (for instance the power cord). Instead, itcorrects mutual phase shifts between the signals taken from the two armsof the dipole.

The invention can assume several practical forms of execution. It willbe better understood by referring to the drawings, in which:

FIG. 1 is a schematic diagram of a differential input transformer andvertical dipole antenna, using a power cord and adjustable delay line inplace of its customary lower arm,

FIG. 2 is a schematic diagram of a similar antenna system, having thedelay line relocated in the dipoles upper arm,

FIG. 3 is a schematic diagram of antenna system having atransformerless, differential input circuit,

FIG. 4 illustrates a stepless delay line with distributed inductances,and

FIGS. 5-8 illustrate various other delay lines with lumped inductancesand capacitances, creating either positive or negative delays.

FIGS. 9 and 10 show examples of simplified, single step, delay lines forpositive or negative delay, while FIG. 11 shows the present inventionapplied to a semi-flexible, semi-grounded dipole, one arm of which issubject to phase-randomness while extracting signal energy from space.

Referring to the antenna system shown in FIG. 1, there is shown anessentially fixed vertical monopole 1, having its effective heightincreased by a capacitive termination 2. Monopole 1 together with powercord 3 forms a dipole which, if the power cord hangs straight down fromthe receiver, is a true, vertical dipole. On the other hand, if the cord3 leaves the receiver in a horizontal direction, the combinationrepresents an oddly tilted dipole. In either case, the signals deliveredto the input terminals 4 and 5 of the differential antenna transformer 6may or may not be in phase-opposition, as they should be, if the largestpossible signal is to be delivered to the input of the RF amplifier 7through lead 8.

The power cord 3 is RF-isolated from the sets chassis (not shown) byinductors 9 and 10, as well as blocking condensers 11, 12 and 13. Acontinuously variable delay line 14 is inserted in series with blockingcapacitor 13 and the lower differential transformer input terminal 5.The control knob or bar (not shown) of variable delay line 14 isaccessible from the outside of the set. The control knob may be markedAerial and can be used in exactly the same manner in which an indoorantenna would customarily be rotated for optimum performance.

Assuming, for instance, that the cord 3 hangs vertically, and that itslength plus incidental capacitive termination, created by the poweroutlet, causes it to have an effective antenna height of wavelength,while a given frequency is received, and that the fixed, capacitivelyterminated monopole 1 has an effective height of A wavelength, thesignals arriving at the differential input terminals 4 and 5 of theantenna transformer 6 would, if any signal delays in the upper and lowerantenna leads (including delay line 14) are identical, be in exactphaseagreement. The transformers differential characteristics would thencause the two signals to cancel out, unless a phase correction isincluded to make reception possible.

The reason for phase agreement between leads 4 and 5, in spite ofdifferent effective antenna heights A and wavelengths) is that the twopoints of signal-origin face the point of reference, between thetransformer input terminals, in opposite directions: the upper signalfaces down, the lower up.

If sufficient delay range is provided in the adjustable delay line 14,the desired perfect phase-opposition at the transformers input terminalscan always be achieved by adjusting the amount of delay, in accordancewith varying frequencies received, varying reflector and re-radiatoreffects, and cord positions.

The circuit in FIG. 2 is nearly identical with the circuit in FIG. 1.Only the location of the delay line has been altered: in FIG. 1 it is inseries with the line-cord antenna, in FIG. 2 in series with the upper,fixed antenna. Corresponding components are identified by identicalnumbers.

FIG. 3 illustrates the obvious fact that the invention is not restrictedto differential antennan transformers. The dual triode 21 shown here hastwo input grids 24 and 25 which take the place of input terminals 4 and5 of the differential antenna transformer in FIGS. 1 and 2. Components,corresponding to FIGS. 1 and 2, are identified in FIG. 3 by identicalnumbers. The adjustable delay line 14 is not shown in FIG. 3, only itsalternative locations D or D in the upper or lower aerial leads, H

respectively.

The delay line itself can assume many forms of which some examples aregiven in FIGS. 4 through 8.

The delay line shown in FIG. 4 is a sufficiently large wire loop 31having a signal input at 36, and having in its center a pivot 32, fromwhich the output signal is taken. Attached to the pivot 32, is an arm 33carrying a metallic cylinder 34, which is insulated from the wire loop31 by cylinder 35, and slides the metallic cylinder 34 along thecircumference of the loop, as the pivot 32 is rotated. The signal iscapacitatively transferred from the loop 31 to the cylinder 34, and thedesired delay, i.e., the delay which minimizes signal cancellationbetween the upper and lower sections of the dipole, can be adjusted byrotating the pivoted arm 33 and thereby varying the length of loopincluded between the signal input 36 and the signal output at the pivot32.

The delay line shown in schematic form in FIG. 5 uses lumped inductors41, 42 46 and capacities 46, 47 50, in conjunction with a selectorswitch 51, as means for selection of optimum delay. The capacities canbe discrete or incidental (condensers or stray capacities).

The delay line shown in schematic form in FIG. 6 also uses lumpedcapacitive and inductive reactances, identified by numbers correspondingto those in FIG. 5. However, the capacities or condensers 46, 47 50 arenot grounded directly, as in FIG. 5, but are grounded through anadjustable capacitor 61 which adjusts the delay in the following manner:Adjustable grounding capacitor 61 is appreciably larger than theremaining capacities, and will therefore effectively ground busbar 62 towhich all delay line capacities are referred, either by directconnection or through mutual capacity. Busbar 62 can be a wire, ametallic frame, or a near-ground surface etc. In its maximum capacityposition, grounding capacitor 61 creates a maximum delay, and in itsminimum position, a minimum delay. The latter is true because capacitors46, 47 50 act as partial shunts of inductors 42, 43, 44 and 45, sinceeach pair of adjacent condencers, being series-connected acts as such ashunting capacity.

The delay line of FIG. 7 is similar to that of FIG. 5, except that thelocation of the delay line inductors and capacitors are reversed. Thiscauses a negative rather than positive delay which, if sufficient delayrange is provided, is equally useful for the purpose of proper signalphasing between the upper and lower dipole sections. The components ofthe delay line of FIG. 7 are designated by the same numbers as thecomponents in FIG. 5.

The delay line of FIG. 8 is similar to that of FIG. 6 with the exceptionthat the locations of the inductors and capacitors are reversed. Busbar62 is grounded through a variable inductor 71 which, at its minimuminductance position, effectively grounds inductors 41, 42 45,

causing maximum negative delay, and at its maximum inductance position,causes minimum delay. The individual inductors 41, 42, 43 and 44, beingseries connected, act as shunts of the in-line condensers 47, 48, 49 and50, causing the negative delay to be a minimum.

FIG. 9 shows a dipole antenna system including a single step L/C-delayline operating near resonance which is a simplification of the lumpedreactance delay line of FIG. 5. It sacrifices a minor amount of signalamplitude which, in view of the greater seriousness of signal cancellingphase errors, can usually be tolerated.

A single step L/C-delay line, near resonance, creates only a 3 dbamplitude loss between plus/minus 45 phase shift limits, or if one 3 dbextreme is used as the zero delay reference.

As shown in FIG. 9 the single step L/C-delay line is inserted into thelower dipole lead. It consists of adjustable inductor 91 and fixedcapacitance 92. The latter may, as before, be either discrete orincidental. If discrete, it may be made adjustable and inductor 91 canbe fixed, or both can be made adjustable, to provide a large phase rangewithout increasing maximum amplitude 1085.

FIG. 10 illustrates a dipole antenna system including a single stepnegative delay line achieved by the reversal of the locations ofcapacity 92 and inductance 91, of the delay line of FIG. 9.

The present invention is not limited to the use of a power cord as thesecond arm of a dipole, the first arm of which is essentially in a fixedposition. Other electric cords, metallic stands and metallic furniture,ear phone cords etc. can take the place of the power cord, and theirsignals brought into proper phase relationship with the dipoles fixedarm. Neither is our invention restricted to vertical dipoles, whetherpartially capacitively terminated, as shown in the drawings, or not.Horizontal dipoles, having one fixed and one randomly placed arm, fallwithin the scope of our invention, including the special case of thehalf-grounded, half-mobile dipole shown in FIG. 11.

The dipole shown in FIG. 11 consists of an upper arm 101, composed ofvertical lead 102 and capacitive termination 103, which is in anessentially fixed position with reference to point A, the midpointbetween the input terminals 4 and 5 of the differential antennatransformer; its other, lower arm 104 consists of two sections 105 and106. The first of these sections, 105, is the chassis, which, is fixedwith reference to point A, the other 106 is the power cord which canassume various positions in random fashion. The electrical center ofthis combination, point B, is subject to random shifts which, are causedby random placement of the combinations mobile part, cord 106. Thus theelectrical vector A-B of the lower arm of the dipole can change itsdirection and length to a new position A-C, if the cord 106 is shiftedto a new position 107. If wave length, chassis size, cord position andcord length happen to coincide unfavorably, total or nearly totalcancellation of the signals in the two transformer input leads 4 and 5is possible, in spite of the fact that lead 5 is grounded to the chassisand lead 4 is not. This experimentally confirmed problem can best beexplained as follows:

(1) It is virtually impossible to ground the input transformer to apoint on the chassis which coincides with its electrical center(exclusive of the cord) D in such manner that the ideal ground point Ain the transformer, which is its electrical center between its inputterminals 4 and 5, coincides physically with point D. This would have tobe a connection without length and without reactive as well as resistiveproperties, impossible to produce, the more so since the true locationof neither A nor D can be pin-pointed.

(2) Even if it could be pin-pointed, it would change with frequency inview of unavoidable imperfections of the transformer and othercontingencies.

(3) The chassis to which input lead 5 is grounded is, in reality, anaerial which is linked with signals and space, both capacitively andinductively. In the absence of the ideal ground connection betweenchassis and antenna transformer a signal voltage can therefore developbetween A and the physical grounding point B of input lead 5, and asignificant current can flow in this lead, the more so since theradiation resistance of the chassis, due to its bulk, is relatively low.

This undesired capability of the chassis to act as an antenna is greatlyenhanced if the power cord is RF grounded to it, as often found insmall, transformerless receivers. Even if no intentional grounding isprovided, stray capacities are usually sufficient to cause the powercord to be included in the overall contour of the chassis, acting as anantenna. Due to the cords physical shape its effect upon chassis contouris increased many times beyond the simple volumetric or surfaceincrease. The cord being roughly shaped like a linear antenna isactually capable of pumping a substantial amount of signal energy intothe chassis, making the half-grounded dipole in FIG. 11 respond torandom cord placement in almost the same manner in which the floatingdipoles in FIGS. 1, 2 and 3 respond, as far as random phase shifts andaccidental signal concellations are concerned.

An adjustable positive or negative delay line 14, in FIG. 11, therefore,can eliminate the signal cancellation problem in a semi-grounded,semi-flexible dipole (whether vertical or horizontal) in the same manneras it solves this problemin floating, semi-flexible dipoles. The delayline can, again, be located either in the signal path of the power cord,as shown, or in the upper antenna lead. It can also be located in leadF-G, physically grounding the differential input to the chassis.

Although the present invention has been illustrated by reference toseveral preferred embodiments, it will be appreciated by those skilledin the art that the present invention is not limited to suchembodiments. It will further be apparent to those skilled in the artthat other modifications and adaptations of the apparatus may be madewithout departing from the spirit and scope of the invention as setforth with particularity in the appended claims.

What is claimed is:

1. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a differential signal input device, and a variable delayline connected between at least one of said arms and said differentialsignal input device for maintaining the signals from said armssubstantially in phase opposition, said variable delay line comprisingan output conductor, an input conductor disposed about the periphery ofa circle, a movable arm pivoted at the center of said circle, a couplingdevice connected to said output conductor and mounted on said movablearm in sliding engagement with said input conductor for coupling signalsfrom said input conductor to said output conductor.

2. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a differential signal input device, and a variable phaseretarding delay line connected between at least one of said arms andsaid diflerential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said variable phaseretarding delay line comprising a plurality of series connectedinductors, a plurality of capacitors connecting the junctions betweensaid inductors to ground, and a selector switch for selective connectionto the junctions between said inductors.

3. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a dilferential signal input device, and a variable phaseretarding delay line connected between at least one of said arms andsaid ditferential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said variable phaseretarding delay line comprising a plurality of series connectedinductors and a plurality of capacitors connecting the junctions betweensaid inductors to ground through a relatively larger variable capacitor.

4. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a differential signal input device, and a variable phaseretarding delay line connected between at least one of said arms andsaid dilferential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said variable phaseretarding delay line comprising a variable inductor connected in seriesbetween said arm and said difierential input signal device, saidvariable inductor being capacitively connected to ground,

5. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a differential signal input device, and a variable phaseadvancing delay line connected between at least one of said arms andsaid differential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said phase advancing delayline comprising a plurality of series connected capacitors, a pluralityof inductors connecting the junctions between said capacitors to ground,and a selector switch for selective connection to the junctions betweensaid capacitors.

6. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a diiferential signal input device, and a variable phaseadvancing delay line connected between at least one of said arms andsaid differential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said variable phaseadvancing delay line comprising a plurality of series connectedcapacitors and a plurality of inductors connecting the junctions betweensaid capacitors to ground through a relatively large inductor.

7. A dipole antenna system comprising a substantially fixed arm and aflexible arm, a diiferential signal input device, and a variable phaseadvancing delay line connected between at least one of said arms andsaid dif ferential signal input device for maintaining the signals fromsaid arms substantially in phase opposition, said variable phaseadvancing delay line comprising a variable capacitor connected in seriesbetween said arm and said differential signal input device, saidvariable capacitor being inductively connected to ground.

References Cited UNITED STATES PATENTS 2,000,529 5/1935 Livingston343-899 XR 2,562,654 7/1951 Williams 343-720 XR 2,666,846 1/1954 Davis343-720 XR 2,911,643 11/1959 Gergely 343-906 XR 2,991,355 7/1961Spindler 343-906 XR OTHER REFERENCES Understanding Amateur Radio,Grammer, The American Radio Relay League, West Hartford, Conn., 1963,TK6550 G7, pages 113-115, 211-213, and 287-289 and title page.

The Radio Amateurs Handbook, The American Radio Relay League, Inc., WestHartford, Conn., 1946, TK6550 R162, page 250.

ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner US. Cl.X.R.

